Dielectric recording medium, and method of and apparatus for producing the same

ABSTRACT

The dielectric recording medium is provided with a dielectric material, a conductive thin film, and a substrate. The conductive thin film and the substrate are bonded by a resin adhesive. The dielectric material is constructed of a ferroelectric single crystal having a uniform thickness, and its one surface is used for a recording and/or reproducing surface, on the order of mm on a side and about 5000 Å thick. The conductive thin film, about 1000 to 2000 Å thick, is placed on a surrounding portion and a back surface of the recording and/or reproducing surface of the dielectric material. The substrate is intended to preserve the thin dielectric material and maintain the planarity, and concave portions are formed on the adhesive surface. The concave portions absorb excessive resin adhesive when the dielectric material is bonded onto the substrate, which makes the adhesive surface uniform and flat.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a dielectric recording mediumfor recording information in a dielectric material, and a method of andan apparatus for producing the dielectric recording medium.

[0003] 2. Description of the Related Art

[0004] Recently, many types of dielectric materials have been developed,and most of them are used for ultrasonic elements, optical elements, amemory and the like. In accordance with the fact, a method of measuringa spontaneous polarization distribution of the dielectric material andlocal anisotropy of the piezoelectric material has been developed. Also,by using this technique, techniques of recording information in thedielectric material and reproducing the information have been developed.

[0005] In order to record information in the dielectric material, apolarization direction of the polarization domain of the dielectricsubstance is formed such that the polarization direction corresponds tothe information. For example, when using as a recording medium aferroelectric bulk single crystal such as LiTaO₃, which has a 180-degreedomain, the Z-cut single crystal is mechanically polished to prepare athin film, and then, its back surface is applied onto a conductorsubstrate with a conductive paste to hold. The medium as formed above isused as a dielectric recording medium.

[0006] Alternatively, after the back surface of a crystal material ofthe dielectric substance is applied onto the conductor substrate withthe conductive paste to hold, a thin crystal is formed by ion beametching or the like from the side of the front surface. The medium asformed above is also used as the dielectric recording medium.

[0007] As described above, in order to record information in highdensity in a microdomain, it is necessary to form the recording mediumas thin as possible, as well as to make the diameter of a probe forrecording and/or reproducing small. Therefore, the mechanical polishing,the etching with ion beam and the like are conventionally used toprepare the thin film.

[0008] However, the method by the mechanical polishing is limited inthinning the medium with a thickness on the order of several μm, evenusing an angle polishing method of polishing a crystal with its backsurface inclined slightly to the surface of a polishing apparatus. It isalso difficult to make it thinner while keeping a stable form becausethe lack of crystal strength causes fracture.

[0009] Moreover, in order to polish the crystal to be in a predeterminedthickness, it is necessary to measure the crystal thickness directly inthe middle of polishing, as occasion demands. However, it takes a longtime to measure it. Especially, in the case of treating a large crystalwhose one side is on the order of mm, it is extremely difficult topolish all of the crystal surfaces in a uniform thickness to prepare thethin film.

SUMMARY OF THE INVENTION

[0010] It is therefore an object of the present invention to provide adielectric recording medium having a recording device constructed by asingle-crystal dielectric material appropriate for high-densityrecording, which is extremely thin and which is also large, for example,on the order of mm on a side, as well as a method of and an apparatusfor producing the dielectric recording medium.

[0011] The above object of the present invention can be achieved by adielectric recording medium for recording information in a dielectricmaterial. The dielectric recording medium is provided with: a substrate;a dielectric material having a predetermined thickness and having arecording surface for recording the information thereon; and an electricconductor provided on at least a back surface of the dielectric materialwhich is on the opposite side to the recording surface. In thedielectric recording medium, the back surface of the dielectric materialon which the electric conductor is provided is bonded to a bondingsurface of the substrate.

[0012] According to the dielectric recording medium of the presentinvention, the electric conductor is placed on the back surface of thedielectric material having a predetermined thickness. A predeterminedelectric potential is set in the electric conductor. For example, theelectric conductor may be connected to the ground. When a probe abuts onthe surface and a voltage is applied, a polarization domain is formed inthe dielectric material on the basis of an electric field generatedbetween the probe and the electric conductor, and thus, information isrecorded.

[0013] The dielectric material is bonded to the bonding surface of thesubstrate through the electric conductor. Since the substrate is hard,even if the recording surface of the dielectric material is large andthe thickness of the dielectric material is thin, the planarity of therecording surface can be ensured and mechanical strength of thedielectric material can be substantially obtained as well.

[0014] In one aspect of the dielectric recording medium of the presentinvention, the electric conductor covers the whole of the back surfaceand a side surface of the dielectric material, and an edge portion ofthe electric conductor is located at a peripheral portion of therecording surface of the dielectric material. Preferably, all of theside surface of the dielectric material may be covered with the electricconductor, and the peripheral portion of the recording surface of thedielectric material may be surrounded with the edge portion of theelectric conductor.

[0015] According to this aspect, the edge portion of the electricconductor is located at the peripheral portion of the recording surface.The edge portion of the electric conductor is connected with the mainbody of the electric conductor covering the back surface of thedielectric material through the electric conductor covering a sidesurface of the dielectric material. Therefore, the same electricpotential as that of the main body of the electric conductor is set inthe edge portion of the electric conductor. If the probe moves out ofthe recording surface, the probe contacts with the edge portion of theelectric conductor. Therefore, the fact that the probe moves out of therecording surface can be electrically detected. Thus, the moving of theprobe can be controlled on the basis of a result of the detection. Ifthe edge portion of the electric conductor is arranged so as to surroundthe recording surface, the fact that the probe moves out of therecording surface can be detected in all directions. Moreover, accordingto this aspect, since the edge portion of the electric conductor islocated at the peripheral portion of the recording surface, it ispossible to remove electric charge on the recording surface rapidly. Ifthe edge portion of the electric conductor is arranged so as to surroundthe peripheral portion of the recording surface, the ability to removethe electric charge can be improved.

[0016] In another aspect of the dielectric recording medium of thepresent invention, the electric conductor is provided with: a firstelectric conductor portion located on the back surface of the dielectricmaterial; a second electric conductor portion located on a side surfaceof the dielectric material and connected with the first electricconductor portion; and a third electric conductor portion located at aperipheral portion of the recording surface of the dielectric materialand connected with the second electric conductor portion. Preferably,all of the side surfaces of the dielectric material may be covered withthe second electric conductor portion, and the peripheral portion of therecording surface may be surrounded with the third electric conductorportion.

[0017] According to this aspect, the third electric conductor portion islocated at the peripheral portion of the recording surface. The thirdelectric conductor portion is connected with the first electricconductor portion located on the back surface of the dielectric materialthrough the second electric conductor portion located on a side surfaceof the dielectric material. Therefore, the same electric potential asthat of the first electric conductor portion is set in the thirdelectric conductor portion. If the probe moves out of the recordingsurface, the probe contacts with the third electric conductor portion.Therefore, the fact that the probe moves out of the recording surfacecan be electrically detected. Thus, the moving of the probe can becontrolled on the basis of a result of the detection. If the thirdelectric conductor portion is arranged so as to surround the peripheralportion of the recording surface, the fact that the probe moves out ofthe recording surface can be detected in all directions. Moreover,according to this aspect, since the third electric conductor portion islocated at the peripheral portion of the recording surface, it ispossible to remove electric charge on the recording surface rapidly. Ifthe third electric conductor portion is arranged so as to surround theperipheral portion of the recording surface, the ability to remove theelectric charge can be improved.

[0018] In another aspect of the dielectric recording medium of thepresent invention, the substrate is a silicon substrate.

[0019] According to this aspect, the silicon substrate is chemicallystable and hardly changes in shape thermally. Using the siliconsubstrate gives a major effect on maintaining the planarity of therecording surface and protecting from mechanical destruction.

[0020] In another aspect of the dielectric recording medium of thepresent invention, a concave portion is provided for the bonding surfaceof the substrate.

[0021] According to this aspect, if the dielectric material is bonded tothe bonding surface of the substrate, excessive adhesive enters theconcave portion. Therefore, the excessive adhesive can be substantiallyabsorbed into the bonding surface of the substrate, and thus, theflatness of an adhesive surface can be ensured. The concave portion canbe formed by performing a mechanical process or an etching process. Forexample, grooves formed with a mechanical device or an etching devicemay be used as the concave portions. Alternatively, the concave portionscan be formed by roughening the bonding surface by performing amechanical process or a chemical process.

[0022] In another aspect of the dielectric recording medium of thepresent invention, the back surface of the dielectric material is bondedto the bonding surface of the substrate by using a resin adhesive.

[0023] According to this aspect, even if the recording surface of thedielectric material is large and the thickness of the dielectricmaterial is thin, it is possible to bond the dielectric material firmlyto the substrate with the flatness ensured.

[0024] In another aspect of the dielectric recording medium of thepresent invention, the dielectric material is a ferroelectric material.

[0025] According to this aspect, since the ferroelectric material isused as the dielectric material, it is possible to make the presence orthe absence of the recorded information precise in the polarizationdomain. Therefore, the recording and the reproducing are well performed.

[0026] In another aspect of the dielectric recording medium of thepresent invention, the dielectric material is LiTaO₃.

[0027] According to this aspect, a Z-cut LiTaO₃ may be used as thedielectric material. Since the dielectric constant of LiTaO₃ is low, thepolarization is easily reversed by the application of the electricfield. Therefore, it is possible to make the presence or the absence ofthe recorded information precise in the polarization domain. Thus, therecording and the reproducing are well performed.

[0028] The above object of the present invention can be achieved by amethod of producing a dielectric recording medium for recordinginformation in a dielectric material. The method is provided with: amask formation process of forming a mask on a first surface of thedielectric material to cover a recording area with the mask; a firstetching process of etching the first surface of dielectric material toremove a predetermined amount of the dielectric material located in anarea which is not covered with the mask; a mask removing process ofremoving the mask from the first surface of the dielectric material; aconductor formation process of forming a conductive thin film over thewhole of the first surface of the dielectric material; a bonding processof bonding the first surface of the dielectric material over which theconductive thin film is formed to a bonding surface of a substrate; anda second etching process of etching a second surface of the dielectricmaterial which is on the opposite side to the first surface.

[0029] According to this method, it is possible to mass-produce theultrathin dielectric recording medium of the present invention in highquality and at a low price.

[0030] In the mask formation process, a mask is formed on the firstsurface of the dielectric material to cover a recording area with themask. The location of the recording area corresponds to the location ofthe recording surface of the dielectric recording medium for recordinginformation thereon. The recording area is defined by forming the maskthereon. A mask preparation method that is generally used may be used.In the case of preparing a single dielectric recording medium, the maskis formed so as to cover one recording area. In the case of preparing aplurality of dielectric recording media, a plurality of masks are formedso as to cover the respective recording areas. In this case, therespective recording areas (i.e. the respective masks) are arranged withspaces between them necessary for cutting the dielectric material todivide the dielectric material (with the substrate, etc.) into theindividual dielectric recording medium.

[0031] In the first etching process, the first surface of the dielectricmaterial is etched to remove a predetermined amount of the dielectricmaterial located in an area which is not covered with the mask. Sincethe mask covers the recording area, the peripheral portion of therecording area is removed by a predetermined depth. This depthcorresponds to the thickness of the recording medium. After this etchingprocess, the mask is removed from the first surface of the dielectricmaterial.

[0032] In the conductor formation process, the conductive thin film isformed over the whole of the first surface of the dielectric materialwhich is etched in the first etching process. This surface correspondsto the back surface of the dielectric material. A method of vacuumdeposition, sputtering, CVD (Chemical Vapor Deposition), or the like canbe used for forming this conductive thin film. This conductive thin filmcorresponds to the electric conductor of the dielectric recordingmedium.

[0033] In the bonding process, the first surface of the dielectricmaterial over which the conductive thin film is formed to the bondingsurface of the substrate. A resin adhesive can be used by bonding thesesurfaces. By firmly bonding the dielectric material having theconductive thin film thereon to the substrate, it is possible to ensurethe strength and the planarity on the dielectric recording medium.

[0034] In the second etching process, the second surface of thedielectric material is etched. The second surface is on the oppositeside to the first surface. This etched surface becomes the recordingsurface of the dielectric recording medium. The etching is performeduntil the conductive thin film located at the peripheral portion of therecording area (i.e., recording surface) is exposed. The conductive thinfilm exposed by this etching becomes the electric conductor located atthe peripheral portion of the recording surface of the dielectricmaterial (i.e., the edged portion of the electric conductor or the thirdelectric conductor portion).

[0035] In one aspect of the method of producing the dielectric recordingmedium of the present invention, a plurality of the recording areasexist on the first surface, and the method is further provided with adivision process of dividing a structure produced by bonding thedielectric material and the substrate to each other into a plurality ofparts so as to separate the plurality of the recording areas from eachother, after the second etching process.

[0036] According to this aspect, in the case of forming the plurality ofdielectric recording media, they are cut and divided into individualdielectric recording media along the space between the recording areasafter the second etching process. Laser and dicing may be used for thedivision.

[0037] In another aspect of the method of producing the dielectricrecording medium of the present invention, the method is furtherprovided with: a measurement process of measuring an etched amount ofthe dielectric material in the second etching process; and a controlprocess of controlling the second etching process on the basis of theetched amount measured by said measurement process.

[0038] According to this aspect, in the measurement process, an amountetched by the second etching process is measured. Alternatively, themeasurement process can be achieved by detecting that the conductivethin film is exposed. As a measurement device or a detection device, amagnetic device, an electric device, an optical device and the like maybe used. In the control process, the second etching process iscontrolled on the basis of the result measured or detected in themeasurement process. By this, if it is confirmed that the conductivethin film located at the peripheral portion of the recording area isexposed, the etching is stopped. In this manner, it is possible tocontrol an accurate etched amount.

[0039] In another aspect of the method of producing the dielectricrecording medium of the present invention, the method is furtherprovided with: a concave portion formation process of forming a concaveportion on the bonding surface of the substrate before the bondingprocess.

[0040] According to this aspect, before the dielectric material isbonded, the concave portion for absorbing excessive adhesive is formedon the surface of the substrate. It is possible to form this concaveportion using the mechanical device, the etching device and the chemicaldevice.

[0041] In another aspect of the method of producing the dielectricrecording medium of the present invention, in the first etching process,the first surface of dielectric material is etched by dry etchingmethod.

[0042] According to this aspect, a dry etching method is used for theetching the first surface of the dielectric material. By using the dryetching method, it is possible to etch the first surface accurately tobe in a predetermined depth, with the recording area left

[0043] In another aspect of the method of producing the dielectricrecording medium of the present invention, in the second etchingprocess, the second surface of the dielectric material is polished bymechanical polishing method.

[0044] According to this aspect, it is possible to quickly etch thedielectric material until reaching the conductive thin film.

[0045] In another aspect of the method of producing the dielectricrecording medium of the present invention, the second etching process isprovided with: a mechanical polishing process of polishing the secondsurface of the dielectric material by using a mechanical polishingmethod; and a dry etching process of etching the second surface polishedin the mechanical polishing process by using a dry etching method.

[0046] According to this aspect, in the etching of the dielectricmaterial until reaching the conductive thin film located at theperipheral portion of the recording area, firstly, the dielectricmaterial can be quickly polished by the mechanical polishing with thepredetermined thickness left, which does not reach the conductive thinfilm. Secondly, the dielectric material can be accurately etched by thedry etching, whose etching rate is slower than that of the mechanicalpolishing and which can precisely and easily control the etched amount,until the conductive thin film appears.

[0047] In another aspect of the method of producing the dielectricrecording medium of the present invention, the method is furtherprovided with: a wet etching process of performing wet etching after thedry etching process.

[0048] According to this aspect, this wet etching aims at the removal ofthe final affected layer. It is possible to remove a portion in whichthe crystalline deteriorates due to the fabrication process of thesubstrate, and thus it is possible to bring out the ferroelectricity ofa sheet of the crystal in a good condition.

[0049] The above object of the present invention can be achieved by anapparatus for producing a dielectric recording medium for recordinginformation in a dielectric material. The apparatus is provided with: amask formation device for forming a mask on a first surface of thedielectric material to cover a recording area with the mask; a firstetching device for etching the first surface of dielectric material toremove a predetermined amount of the dielectric material located in anarea which is not covered with the mask; a mask removing device forremoving the mask from the first surface of the dielectric material; aconductor formation device for forming a conductive thin film over thewhole of the first surface of the dielectric material; a bonding devicefor bonding the first surface of the dielectric material over which theconductive thin film is formed to a bonding surface of a substrate; anda second etching device for etching a second surface of the dielectricmaterial which is on the opposite side to the first surface.

[0050] According to the apparatus of the present invention, it ispossible to mass-produce the ultrathin dielectric recording medium ofthe present invention in high quality and at a low price.

[0051] The mask formation device forms a mask on the first surface ofthe dielectric material to cover a recording area with the mask. A maskpreparation method that is generally used may be used.

[0052] The first etching device etches the first surface of thedielectric material to remove a predetermined amount of the dielectricmaterial located in an area which is not covered with the mask by apredetermined depth. This depth corresponds to the thickness of therecording medium. As this first etching device, there are an ECR(Electron Cyclotron Resonance) etching apparatus, an RIE (Reactive IonEtching) etching apparatus, an ion beam etching apparatus and the like.Using such a etching apparatus, it is possible to etch the dielectricmaterial accurately. Even an oxide material, such as LiTaO₃, allows thedry etching in a good condition.

[0053] The conductor formation device forms the conductor thin film overthe whole of the first surface of the dielectric material etched by thefirst etching device. A vacuum deposition apparatus, a sputteringapparatus, a CVD apparatus or the like can be used for forming theconductive thin film.

[0054] The bonding device bonds the first surface of the dielectricmaterial over which the conductive thin film is formed to the bondingsurface of the substrate. A resin adhesive can be used as an adhesive.

[0055] The second etching device etches the second surface of thedielectric material which is on the opposite side to the first surface,until the conductive thin film located at the peripheral portion of therecording area is exposed.

[0056] In one aspect of the apparatus for producing the dielectricrecording medium of the present invention, a plurality of the recordingareas exist on the first surface, and the apparatus further providedwith a division device for dividing a structure produced by bonding thedielectric material and the substrate to each other into a plurality ofparts so as to separate the plurality of the recording areas from eachother, after an etching process with the second etching device.

[0057] According to this aspect, in the case of forming the plurality ofdielectric recording media, they are cut and divided into individualdielectric recording media along the spaces between the recording areasby using the division device such as laser device and dicing device.

[0058] In another aspect of the apparatus for producing the dielectricrecording medium of the present invention, the apparatus is furtherprovided with: a measurement device for measuring an etched amount ofthe dielectric material; and a control device for controlling the secondetching device on the basis of the etched amount measured by saidmeasurement device.

[0059] According to this aspect, the measurement device measures anamount etched by the second etching device, or it detects that theconductive thin film is exposed. As the measurement device, an analysisdevice, such as a magnetic device, an electric device, an opticaldevice, and a Q-mass (Quadrupole Mass spectrometer), may be used. Forexample, in an analysis of emission spectrum, when the etching of thedielectric material goes on, the composition of the conductive thin filmis included in the emission spectrum of plasma, which means theconductive thin film is exposed. That is how to detect the etchedamount. The control device controls the second etching device on thebasis of the result measured by the measurement device. By this, if itis confirmed that the conductive thin film located at the peripheralportion of the recording area is exposed, the etching is stopped.

[0060] In another aspect of the apparatus for producing the dielectricrecording medium of the present invention, the apparatus is furtherprovided with a concave portion formation device for forming a concaveportion on the bonding surface of the substrate before a bonding processwith the bonding device.

[0061] According to this aspect, before the dielectric material isbonded to the substrate, the concave portion for absorbing excessiveadhesive is formed.

[0062] In another aspect of the apparatus for producing the dielectricrecording medium of the present invention, the second etching device isprovided with: a mechanical polishing device for polishing the secondsurface of the dielectric material by mechanical polishing method; and adry etching device for etching the second surface polished in themechanical polishing process by dry etching method.

[0063] According to this aspect, in the etching of the dielectricmaterial until reaching the conductive thin film, firstly, thedielectric material can be quickly polished by the mechanical polishingdevice with the predetermined thickness left, which does not reach theconductive thin film. Secondly, the dielectric material can beaccurately etched by the dry etching, until the conductive thin filmsurrounding the recording area appears.

[0064] The nature, utility, and further features of this invention willbe more clearly apparent from the following detailed description withreference to preferred embodiments of the invention when read inconjunction with the accompanying drawings briefly described below.

BRIEF DESCRIPTION OF THE DRAWINGS

[0065]FIG. 1A is a plan view showing a first embodiment of thedielectric recording medium of the present invention;

[0066]FIG. 1B is an A-A cross sectional side view of FIG. 1A;

[0067]FIG. 2A is a plan view showing a second embodiment of thedielectric recording medium of the present invention;

[0068]FIG. 2B is a B-B cross sectional side view of FIG. 2A;

[0069]FIG. 3A is a plan view showing the preparation of the dielectricrecording media shown in FIG. 2A and FIG. 2B;

[0070]FIG. 3B is a C-C cross sectional side view of FIG. 3A;

[0071]FIG. 4A and FIG. 4B are plan views showing the preparation formsof the dielectric recording medium of the present invention, FIG. 4Ashowing a mask layout in the case of a single dielectric recordingmedium, and FIG. 4B showing a mask layout in the case of a plurality ofdielectric recording media;

[0072]FIG. 5A to FIG. 5D are cross sectional views showing processes ofproducing the dielectric recording medium of the present invention, FIG.5A showing a dielectric material, FIG. 5B showing such a condition thata resist is disposed on the dielectric material, FIG. 5C showing such acondition that etching is performed, and FIG. 5D showing such acondition that the resist is removed;

[0073]FIG. 6A to FIG. 6D are cross sectional views showing processes ofproducing, which follows FIG. 5D, FIG. 6A showing such a condition thata conductive thin film is formed on the etched surface, FIG. 6B showingsuch a condition that the conductive-thin-film-formed surface is bondedto a substrate, FIG. 6C showing such a condition that the dielectricmaterial is polished by mechanical polishing, and FIG. 6D showing such acondition that the dielectric material is etched by plasma etching afterthe mechanical polishing;

[0074]FIG. 7A and FIG. 7B are schematic diagrams showing bonding surfaceconditions of the substrate, FIG. 7A showing such a condition thatgrooves are provided, and FIG. 7B showing such a condition that thesurface is roughened and that concave portions are formed;

[0075]FIG. 8 is a schematic diagram showing one example of a chemicalmechanical polishing apparatus;

[0076]FIG. 9 is a schematic diagram showing an ECR etching apparatus,which is one example of a dry etching apparatus;

[0077]FIG. 10 is a schematic diagram showing a relationship between athickness of the dielectric substance and a minimum voltage, whichreverses a polarization domain, with a probe radius as a parameter, inthe case of using a Z-cut LiTaO₃ single crystal as a recording material;

[0078]FIG. 11 is a block diagram of an apparatus for producing thedielectric recording medium associated with the present invention; and

[0079]FIG. 12 is a schematic diagram showing one example of aninformation recording/reproducing apparatus using the dielectricrecording medium associated with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0080] (Embodiment Associated with the Dielectric Recording Medium)

[0081] The embodiment of the dielectric recording medium of the presentinvention will be explained with reference to FIG. 1A to FIG. 4B. FIG.1A is a plan view showing a first embodiment of the dielectric recordingmedium of the present invention. FIG. 1B is an A-A cross sectional sideview of FIG. 1A. FIG. 2A is a plan view showing a second embodiment ofthe dielectric recording medium of the present invention. FIG. 2B is aB-B cross sectional side view of FIG. 2A. FIG. 3A is a plan view showingthe preparation of the dielectric recording medium shown in FIG. 2A andFIG. 2B. FIG. 3B is a C-C cross sectional side view of FIG. 3A. FIG. 4Aand FIG. 4B are plan views showing the preparation forms of thedielectric recording medium of the present invention, FIG. 4A showing amask layout in the case of a single dielectric recording medium, andFIG. 4B showing a mask layout in the case of a plurality of dielectricrecording media.

[0082] A dielectric recording medium 1 is constructed, as shown in FIG.1, such that a dielectric material 11, a conductive thin film 12, and asubstrate 13 are laminated and that the conductive thin film 12 and thesubstrate 13 are bonded by a resin adhesive 14.

[0083] The dielectric material 11 is, for example, a ferroelectricsingle crystal having a uniform thickness, and its one surface is usedfor a recording and/or reproducing surface on which a probe forrecording and/or reproducing works. The size of the dielectric material11 is large, such as on the order of mm on a side and about 5000 Åthick, for example. As the material, LiTaO₃ is used, which has a180-degree domain. As the other dielectric materials, the following isconceivable: a PZT material as being a solid solution of PbTiO₃—PbZrO₃;barium titanate represented as BaTiO₃; lithium niobate represented asLiNbO₃; a PLZT material as being a solid solution of lead (Pb), lantern(La), zirconium (Zr), and titanium (Ti); and the like.

[0084] The conductive thin film 12, which is about 1000 to 2000 Å thick,is placed on a surrounding portion of the recording and/or reproducingsurface of the dielectric material 11, except on the recording and/orreproducing surface. This conductive thin film 12 is coated by metalsuch as aluminum by using the method of vacuum deposition, sputtering,CVD or the like, and is connected to the ground of a recording and/orreproducing apparatus. Other than the aluminum, metal such as platinumand an oxide conductive film such as InO₂ which has a good corrosionresistance may be also used.

[0085] The substrate 13 is intended to preserve the thin dielectricmaterial 11 and maintain the planarity of the dielectric material 11.Silicon or the like in a predetermined thickness may be used, forexample. Moreover, concave portions 13 a are formed on the surface forbonding the dielectric material 11 thereto. The concave portions 13 aare relatively large, and they are effective in absorbing excessiveadhesive and forming a uniform and flat adhesive surface when the thindielectric material 11 is bonded onto the substrate 13.

[0086] The resin adhesive 14 is an adhesive for bonding to the substrate13 the dielectric material 11 for which the conductive thin film 12 isprovided. It gives strong adhesion and the flat adhesive surface.

[0087] Furthermore, in order to ensure the convenience of handling thedielectric recording medium 1 having this structure and its strength, amaterial such as plastic or ceramics may be used to package therecording medium except the recording and/or reproducing surface.

[0088] A dielectric recording medium 2 in FIG. 2A and FIG. 2B is in theform that one is cut out of a plurality of dielectric recording media.This medium is produced by using a method of preparing a plurality ofdielectric recording media at a time. The structure and the functions ofthe dielectric recording medium 2 are the same as those of thedielectric recording medium 1 explained with reference to FIG. 1A andFIG. 1B. FIG. 3A and FIG. 3B show four dielectric recording mediaprepared at a time. They are cut off in the last process, and dividedinto dielectric recording media 11 a to 11 d. Masks 15 used for theseproductions are shown in FIG. 4A and FIG. 4B. The dielectric recordingmedium 2 shown in FIG. 2 corresponds to the one which is cut out. It isalso possible to prepare much more dielectric recording media at a time.

[0089] The function of the dielectric recording medium 1 having theabove-described structure as a recording medium is as follows. When avoltage is applied to a probe that abuts on the recording and/orreproducing surface of the dielectric material 11, an electric field isgenerated between the probe and the conductive thin film 12, which is onthe back surface of the dielectric material 11, and the portion on whichthe probe abuts is polarized. By having this polarization reached to theback surface of the dielectric material 11, a stable polarization domainis formed, and information is recorded in it. On the other hand, withrespect to the reproduction, by having the probe abutted on therecording and/or reproducing surface to trace it, a minute volume changecorresponding to the polarization is detected, for example, by anonlinear microscope method, and the recorded information is reproduced.In this case, by initiating the whole medium in advance to a + surfaceor a − surface, it is possible to improve S/N ratio.

[0090] The dielectric recording media 1 and 2 as described above aresuper-high-density recording and/or reproducing media having recordingdensity more than 1 T bits/inch².

[0091] (Embodiment Associated with a Method of Producing the DielectricRecording Medium)

[0092] Next, the method of producing the electric recording medium willbe explained with reference to FIG. 5A to FIG. 7B. Here, the form ofpreparing a plurality of recording media as shown in FIG. 3A and FIG. 3Bwill be explained, but a single recording medium can be prepared in thesame method. FIG. 5A to FIG. 5D are cross sectional views showingprocesses of producing the dielectric recording medium of the presentinvention, FIG. 5A showing a dielectric material, FIG. 5B showing such acondition that a resist is disposed on the dielectric material, FIG. 5Cshowing such a condition that etching is performed, and FIG. 5D showingsuch a condition that the resist is removed. FIG. 6A to FIG. 6D arecross sectional views showing processes of producing, which follows FIG.5D, FIG. 6A showing such a condition that a conductive thin film isformed on the etched surface, FIG. 6B showing such a condition that theconductive-thin-film-formed surface is applied on a substrate, FIG. 6Cshowing such a condition that the dielectric material is polished bymechanical polishing, and FIG. 6D showing such a condition that thedielectric material is etched by plasma etching after the mechanicalpolishing. FIG. 7A and FIG. 7B are schematic diagrams showing bondingsurface conditions of the substrate, FIG. 7A showing such a conditionthat grooves are provided, and FIG. 7B showing such a condition that thesurface is roughened and that concave portions are formed.

[0093] Firstly, as shown in FIG. 6A, as the dielectric material 11, aferroelectric single crystal is used. In the dielectric material 11, thelength of one side is about 10 mm. The thickness is about 0.2 to 0.5 mm.Both surfaces are parallel to each other and mirror-polished. Forexample, a Z-cut LiTaO₃ single crystal is used.

[0094] Secondly, as shown in FIG. 5B, the mask 15 is disposed on onesurface of the dielectric material 11 so as to cover a recording area.The mask 15 may be formed in a method generally used for a metal film, aresist film, a dry resist film or the like.

[0095] Then, as shown in FIG. 5C, by etching such as RIE (Reactive IonEtching), ECR (Electron Cyclotron Resonance) plasma or ion beam, asurrounding portion of the mask 15 is etched to be 0.5 μm or less deep,i.e. it is etched to be about as thick as the recording medium.

[0096] Then, as shown in FIG. 5D, the mask 15 is removed and the depthof the etching is precisely measured using a contact probe profilometer,a laser interferometer or the like. The thickness of the recordingmedium is finally determined on the basis of this depth. The datameasured here is used in the etching process as feedback data.

[0097] Then, as shown in FIG. 6A, the conductive thin film 12 which willbe an electrode of the recording medium is formed on the etched surfacein the method such as sputtering or deposition. As the material of theconductive thin film 12, a metal material, such as aluminum or platinum,and an oxide conductive thin film, such as InO₂ which has a goodcorrosion resistance, may be used.

[0098] Then, as shown in FIG. 6B, the conductive thin film 12 and thesubstrate 13 are bonded by a strong adhesive material, such as the resinadhesive. The substrate 13 may be silicon, for example, and has on itsbonding surface the concave portions 13 a in groove shape as shown inFIG. 7A or the concave portions 13 a formed by its surface beingroughened as shown in FIG. 7B. The concave portions 13 a absorbexcessive adhesive, which makes the adhesive surface uniform and flat.It is necessary to keep a dielectric single crystal having a largerecording surface and thin thickness being the uniform flat surface. Tothis end, the concave portions 13 a are greatly effective. Moreover, theadhesion onto the strong silicon substrate 13 prevents the deformationand the damage of the dielectric single crystal.

[0099] Then, as shown in FIG. 6C, the dielectric material 11 is polishedto be 10 μm or less, for example. Here, when the dielectric material 11is mounted on a polishing apparatus, the adjustment is performed suchthat a surface plate of the polishing apparatus, which will be thereference plane, and an abrasive surface of the dielectric material 11have parallelism at the optical wavelength level. For example, theparallelism is set by using a parallelism adjustment apparatus. In theparallelism adjustment apparatus, the reference plane of the polishingapparatus and a surface holding the dielectric material 11 are held atthree points on the circumference so as to adjust the angle of thereference surface and the holding surface. The adjustment is performedby using an optical flat as the reference surface, for example, and bymaximizing the interval of an interference pattern (a Newton ring) madewith the surface of the dielectric material 11. According to thismethod, even if a parallelism gap occurs between the dielectric material11 and the substrate 13 when the dielectric material 11 is bonded ontothe substrate 13, the parallelism of the both surfaces of the dielectricmaterial 11 by the polishing can be ensured.

[0100] In the abrasive process described above, by firstly carrying outa lapping process using about 1 μm abrasive grains, and then carryingout a CMP (Chemical Mechanical Polishing) process, it is possible toperform finishing with a less affected layer.

[0101] Moreover, as shown in FIG. 6D, by the etching, such as the RIE,the ECR plasma or the ion beam, from the abrasive surface, thedielectric material 11 is etched uniformly, thinly and precisely untilthe conductive thin film 12 appears which is placed on the surroundingportion of the dielectric material 11. With respect to the end pointdetection of the etching, it is possible to detect it with an analysisdevice, such as an emission spectrometer or the Q-mass, when thecomponent elements of the conductive thin film 12 are released into theetching apparatus. When they are detected, the etching is ended.

[0102] The dielectric recording medium as prepared above has an enormousstorage capacity on the order of 1.6 G bits/mm² if the polarizationdomain size is 25 nm which will be record dots, for example.

[0103] Incidentally, wet etching by acid such as hydrofluoric acid maybe performed after the dry etching. This aims at the removal of thefinal affected layer. It is possible to remove a portion in which thecrystalline deteriorates due to the machining of the substrate, and thusit is possible to bring out the ferroelectricity of a sheet of thecrystal in a good condition.

[0104] Next, an example of the CMP used for the method of producing ofthe dielectric recording medium of the present invention will beexplained. As shown in FIG. 8, the dielectric recording medium 2 ispolished by dropping a liquid in which abrasive particles are dispersed,i.e. an abrasive 24, from a nozzle 23 onto an abrasive pad 22, which isapplied on an abrasive table 21, pressing down against the abrasive pad22 the dielectric recording medium 2 mounted on a turntable 25, andspinning the abrasive table 21 and the turntable 25 as shown with arrowsR1 and R2, respectively. The used abrasive particles are minute silicaparticles, alumina particles or the like, on the order of severalhundreds Å. Moreover, with respect to the liquid which disperses theabrasive particles, pH adjustment, electrolyte mixing, abrasive-particledispersion, a state of aggregation and the like are controlled dependingon the abrasive particles and the dielectric material 11.

[0105] Next, an example of an ECR etching apparatus used for the methodof producing the dielectric recording medium of the presentation will beexplained. As shown in FIG. 9, a gas such as Ar is fed into a plasmagenerator 31, and an about 2.5 GHz microwave is applied. To the plasmagenerator 31, a minus DC voltage is applied, and plasma is generated.This plasma moves according to the axial intensity distribution ofmagnetic field formed by an electromagnet 32 placed around thecircumference of the plasma generator 31, accelerates in parallel by anextraction electrode 33, and collides with the dielectric recordingmedium 2 mounted on a holder 35. The dielectric material 11 is etched bythe collision energy. Since the condition of the etching depends on thecollision angle of the plasma, it is designed such that the magneticfield around the holder 35 has a parallel magnetic field distributionand that the dielectric material 11 is irradiated with a plasma fluid,which is a high current, uniform and parallel.

[0106]FIG. 10 is a schematic diagram showing a relationship between athickness of the dielectric substance and a minimum voltage required forreversal of a polarization domain, with a probe shape as a parameter, inthe case of using a Z-cut LiTaO₃ single crystal as the dielectricsubstance. Although FIG.10 shows the relationship in the case that thethickness of the dielectric recording medium and the diameter of the tipportion of the probe are on the order of μm, it is confirmed that if thethickness of the dielectric recording medium and the diameter of the tipportion of the probe are reduced to the order of nm, the relationshipsimilar to that shown in FIG. 10 can be obtained. Since the polarizationdomain corresponding to the recorded information is formed substantiallyin the same size as the diameter of the probe, the diameter ispreferably made small for high-density recording. On the other hand, asfor the voltage required for forming the polarization domain, FIG. 10teaches that as the dielectric material 11 becomes thicker, the requiredvoltage becomes higher. Especially, when the diameter of the probe issmall, the required voltage increases more rapidly, as the thickness ofthe dielectric material 11 increases. Therefore, in order to make theapplied voltage low, e.g. about 10 V, it is necessary to thin down thedielectric material 11, e.g. about 5000 Å. The method of producing thedielectric recording medium of the present invention realizes thisnecessity.

[0107] In the above-described method, the ferroelectric single crystalcan be an ideal ultrathin material, and it is possible to realize therecording medium with high density and high recording capacity whichuses the uniform, flat and large ferroelectric single crystal.

[0108] (Embodiment Associated with an Apparatus for Producing theDielectric Recording Medium)

[0109] The apparatus for producing the dielectric recording medium ofthe present invention shown in FIG. 11 is an apparatus for preparing aplurality of large dielectric recording media in a round of productionprocesses. The apparatus is provided with: a recording area formationdevice 61; a conductive thin film formation device 62; a bonding device63 for bonding the recording medium and the substrate; a substrateformation device 64; a mechanical polisher 65; a dry etching device 66;a polish amount detector 67; an etched amount detector 68; a polishamount controller 69; an etched amount controller 70; and a cuttingdevice 71.

[0110] The recording area formation device 61 disposes the mask forcovering a recording area portion, for example, in order to form fourrecording areas on the dielectric material 11, as shown in FIG. 4B. Themask can be prepared in a general-purpose method. The dielectricmaterial 11 covered with the mask is etched by the ECR plasma, a RIEapparatus or the like, so as to be in a predetermined depth, e.g. about5000 Å, with the record portion left. This etched amount is controlledby detecting the change of a plasma condition or the like, using a gaschromatography measurement, an analysis of emission spectrum andabsorption spectrum of the plasma, a discharge impedance measurement orthe like, which depend on the change of the types and the amounts ofdecomposition and reaction products. When the etching is ended, the maskis removed. The portion from which the mask is removed corresponds tothe portion of the recording surface, and the etching depth correspondsto the thickness of the record portion.

[0111] The conductive thin film formation device 62 forms the conductivethin film 12 in a predetermined thickness on the whole of the surfaceetched at the recording area formation 61. This conductive thin film 12is also formed on the sidewall etched, so that the conductive thin film12 covers the whole surface of the dielectric material 11. Theconductive thin film 12 is formed by using an apparatus for vacuumdeposition, CVD or sputtering. The thickness of the conductive thin film12 is controlled by time control using the deposition or growing rate ofthe thin film, a measurement of electric resistance or the like. As thematerial for forming the conductive thin film 12, metal such as platinumor aluminum, and an oxide conductive substance such as InO₂ are used.

[0112] The bonding device 63 bonds the surface of the dielectricmaterial on which the conductive thin film 12 is formed to the substrate13 using the resin adhesive. The concave portions 13 a are formed on thebonding surface of the substrate 13. Excessive adhesive is absorbed onthese concave portions 13 a, and thus, the bonding surface can ensurethe flatness after the adhesion.

[0113] The substrate formation device 64 provides the concave portions13 a for the bonding surface of the substrate 13. With respect to theformation of these concave portions 13 a, the formation of grooves bymechanical grinding, polishing or etching, a method by chemicalprocessing, or the like is used. These concave portions 13 a areintended to absorb the excessive adhesive and ensure the flatness of theadhesive surface as described above.

[0114] The mechanical polisher 65 is, for example, the above-describedmechanical polishing device as shown in FIG. 8, and it polishes thedielectric material 11 from the opposite surface to the substrate 13until being under a predetermined thickness, e.g. under 10 μm or less.In order to polish a large surface to be in a uniform thickness, theoptical-wavelength-level parallelism is required for the surface planefor polishing and the surface of a test piece. To this end, anadjustment mechanism capable of satisfying this requirement is provided.In this adjustment mechanism, the optical flat may be used, for example,and the adjustment is performed so as to maximize the interval of theinterference pattern made with the surface of the test piece. Asdescribed above, the mechanical polisher 65 is used to ensure theparallelism of the dielectric material 11 and efficiently grind orpolish it.

[0115] The dry etching device 66 finely and precisely etches it untilthe conductive thin film 12 is exposed after the mechanical polishing.As the dry etching, the ECR etching apparatus or the RIE apparatusdescribed above may be used, for example, as shown in FIG. 9.

[0116] The polish amount detector 67 detects the amount polished by themechanical polishing device, and serves to control the mechanical polishamount. As the detection device, it is possible to use a device fordetecting the position of a mechanical portion corresponding to thepolished thickness by using an electric, magnetic or optical scale.

[0117] The etched amount detector 68 detects the amount etched by thedry etching, and serves to control the dry etching. With respect to theend point detection of the etching, it is possible to use the gaschromatography measurement, the analysis of emission spectrum andabsorption spectrum of the plasma, the Q-mass or the like, which dependon the change of the types and the amounts of decomposition and reactionproducts when the conductive thin film 12 is exposed.

[0118] The polish amount controller 69 controls the operation of themechanical polisher 65, on the basis of the polished amount of thepolish amount detector 67. This is intended to set the final etchedamount of the dry etching, and as the etched amount of the dry etchingis smaller, the production time shortens more. Therefore, it ispreferable to gain a more mechanical polish amount within a range not todamage the conductive thin film 12.

[0119] The etched amount controller 70 controls the etched amount of thefinal finishing until the conductive thin film 12 is exposed. Itcontrols, for example, the ECR etching apparatus, on the basis ofdetection data of the etched amount detector 68.

[0120] The cutting device 71 is a device for dividing a plurality of therecording area portions formed by the above-described devices andcompleting a plurality of dielectric recording media. As for thecutting, a cutting device such as laser or dicing may be used.

[0121] The apparatus for preparing the plurality of dielectric recordingmedia at a time was explained above. With respect to the preparation ofthe single dielectric recording medium, it can be prepared using a maskfor a single body at the recording area formation device 61 withoutcarrying out the final process held in the cutting device 71.

[0122] (Embodiment of an Information Recording/Reproducing ApparatusUsing the Dielectric Recording Medium of the Present Invention)

[0123] Next, an information recording/reproducing apparatus 6 using thedielectric recording medium of the present invention will be explainedwith reference to FIG. 12. FIG. 12 is a schematic diagram showing ablock structure of the information recording/reproducing apparatus 6using the dielectric recording medium 1.

[0124] As shown in FIG. 12, the information recording/reproducingapparatus 6 is provided with: the dielectric recording medium 1; a probe50; an electrode 51; an AC (Alternating Current) signal generator 52; arecording signal generator 53; an adder 54; an oscillator 55; a FM(Frequency Modulation) demodulator 56; a signal detector 57; an inductorL; an inductor La; a capacitance Ca; a switch SW 1. In addition, theapparatus 6 further has other devices for performing various generalfunctions of recording and reproducing information.

[0125] The probe 50 is a member having a hemispherical tip with apredetermined radius. At least the surface of the probe 50 hasconductivity to apply a voltage. When information is recorded, thevoltage is applied to the probe 50 to form the polarization domain inthe dielectric recording medium 1. On the other hand, when the recordedinformation is reproduced, the polarization domain is traced by theprobe 50 to pick up the recorded information.

[0126] The electrode 51 is a return electrode for the high-frequencyelectric field that is generated by the oscillator 55 and applied to themicrodomain of the dielectric recording medium 1 through the probe 50.

[0127] The AC signal generator 52 is a device for generating an ACsignal which is applied to the probe 50. The AC signal generator 52applies an alternating electric field to the microdomain of thedielectric substance and modulates reading signals at the time ofreading information so as to ensure the separation of the readingsignals. Moreover, the AC signal generator 52 biases a recording signalfrom the recording signal generator 53 and applies the biased recordingsignal to the probe 50 to record the information. The difference in acapacitance Cs just under the probe 50 corresponding to the polarizationstate causes the oscillation frequency of the oscillator 55 to bemodulated. By demodulating this, it is possible to monitor whether anaccurate recording operation is performed. When the information is readout, the SW1 is connected to the side of a terminal a. When theinformation is written, the SW1 is connected to the side of a terminalb.

[0128] The recording signal generator 53 converts information which isto be recorded in the dielectric recording medium 1 to a signal in theformat appropriate for recording. The voltage level, the pulse width andthe like thereof are also set optimally and are outputted.

[0129] The adder 54 adds the signal for recording from the recordingsignal generator 53 and the AC signal from the AC signal generator 52 tomodulate and apply them to the probe 50.

[0130] The oscillator 55 generates a signal used for the readout of therecorded information by frequency modulation. The oscillation frequencyis set to about 1 GHz, for example.

[0131] The inductor La and the capacitance Ca constitute a low-cut (LC)filter installed in order to prevent the AC signal of the AC signalgenerator 52 from interfering with the oscillator 55. The oscillationfrequency of the oscillator 55 is on the order of 1 GHz, so that even ifthe AC signal of the AC signal generator 52 is on the order of MHz, itis substantially possible to separate them using the simple LC filter.Moreover, increasing the frequency is advantageous in view of datatransfer rate, and in that case, a filter constant appropriate for thecase may be selected.

[0132] The inductor L constitutes a resonance circuit with thecapacitance Cs corresponding to the polarization domain just under theprobe 50. The change of the capacitance Cs causes the change of theresonance frequency, resulting in frequency-modulating the oscillationsignal of the oscillator 55. By demodulating this frequency-modulation,it is possible to read the recorded information. Here, although there isthe capacitance Ca in the resonance circuit, since the capacitance Cs isextremely small as compared to the capacitance Ca, the capacitance Cs isa dominant factor with respect to the resonance frequency.

[0133] The FM demodulator 56 demodulates the oscillation signal of theoscillator 55, which is frequency-modulated by the resonance circuitconstructed with the inductor L and the capacitance Cs. A typical FMdetection device is used for this.

[0134] The signal detector 57 performs coherent (synchronous) detectionon the signal demodulated with the FM demodulator 56, using the ACsignal from the AC signal generator 52 as a synchronization signal, andreproduces the recorded information.

[0135] Next, the record operation of the informationrecording/reproducing apparatus 6 will be explained. The SW1 isconnected to the terminal b. Firstly, information to be recorded isinputted to the recording signal generator 53. In the recording signalgenerator 53, the information to be recorded is converted into apredetermined format appropriate for recording and is outputted as adigital recording signal having the set voltage level and the set pulsewidth.

[0136] The recording signal from the recording signal generator 53 isapplied to the probe 50 via the inductor La. Then, by the electric fieldgenerated between the probe 50 and the electric conductor 12 of thedielectric recording medium 1, the polarization domain is formed in apredetermined portion of the dielectric recording medium 1, resulting inrecording the information.

[0137] Monitoring a recorded information is performed byfrequency-modulating the oscillation frequency of the oscillator 55using the resonance circuit of the inductor L and the capacitance Csjust under the probe 50 corresponding to the formed polarization domain,demodulating this frequency-modulated signal with the FM demodulator 56,and performing a coherent detection at the signal detector 57 with theAC signal of the AC signal generator 52 as the synchronization signal.

[0138] Next, the reproduction operation of the informationrecording/reproducing apparatus 6 will be explained. The SW1 isconnected to the terminal a. To the probe 50, the AC signal is appliedfrom the AC signal generator 52. This AC signal will be thesynchronization signal in the coherent detection. When the probe 50traces on the polarization domain, the capacitance Cs is detected. Theoscillation frequency of the oscillator 55 is modulated by the resonancefrequency of the resonance circuit constructed with the capacitance Csand the inductor L. This frequency-modulated signal is demodulated inthe FM demodulator 56, and the coherent detection is performed in thesignal detector 57 with the AC signal of the AC signal generator 52 asthe synchronization signal, resulting in reproducing the recordinformation.

[0139] The signal picked up in this manner is reproduced with the ACsignal of the AC signal generator 52 as the synchronization signal, andthus the recorded information is reproduced. Incidentally, with respectto a device used for the coherent detection, any device can be used ifit is a device for reproducing a signal synchronously with the AC signalof the AC signal generator 52, such as a lock-in amplifier.

[0140] The invention may be embodied in other specific forms withoutdeparting from the spirit or essential characteristics thereof. Thepresent embodiments are therefore to be considered in all respects asillustrative and not restrictive, the scope of the invention beingindicated by the appended claims rather than by the foregoingdescription and all changes which come within the meaning and range ofequivalency of the claims are therefore intended to be embraced therein.

[0141] The entire disclosure of Japanese Patent Application No.2002-086576 filed on Mar. 26, 2002 including the specification, claims,drawings and summary is incorporated herein by reference in itsentirety.

What is claimed is:
 1. A dielectric recording medium for recording information in a dielectric material, the dielectric recording medium comprising: a substrate; a dielectric material having a predetermined thickness and having a recording surface for recording the information thereon; and an electric conductor provided on at least a back surface of the dielectric material which is on the opposite side to the recording surface, wherein the back surface of the dielectric material on which the electric conductor is provided is bonded to a bonding surface of the substrate.
 2. The dielectric recording medium according to claim 1, wherein the electric conductor covers the whole of the back surface and a side surface of the dielectric material, and an edge portion of the electric conductor is located at a peripheral portion of the recording surface of the dielectric material.
 3. The dielectric recording medium according to claim 2, wherein the electric conductor covers all of the side surfaces of the dielectric material, and the edge portion of the electric conductor surrounds the peripheral portion of the recording surface of the dielectric material.
 4. The dielectric recording medium according to claim 1, wherein the electric conductor comprises: a first electric conductor portion located on the back surface of the dielectric material; a second electric conductor portion located on a side surface of the dielectric material and connected with the first electric conductor portion; and a third electric conductor portion located at a peripheral portion of the recording surface of the dielectric material and connected with the second electric conductor portion.
 5. The dielectric recording medium according to claim 4, wherein the second electric conductor portion covers all of the side surfaces of the dielectric material, and the third electric conductor portion surrounds the peripheral portion of the recording surface of the dielectric material.
 6. The dielectric recording medium according to claim 1, wherein the substrate is a silicon substrate.
 7. The dielectric recording medium according to claim 1, wherein a concave portion is provided on the bonding surface of the substrate.
 8. The dielectric recording medium according to claim 1, wherein the back surface of the dielectric material is bonded to the bonding surface of the substrate by using a resin adhesive.
 9. The dielectric recording medium according to claim 1, wherein said dielectric material is a ferroelectric material.
 10. The dielectric recording medium according to claim 1, wherein said dielectric material is LiTaO₃.
 11. A method of producing a dielectric recording medium for recording information in a dielectric material, the method comprising: a mask formation process of forming a mask on a first surface of the dielectric material to cover a recording area with the mask; a first etching process of etching the first surface of the dielectric material to remove a predetermined amount of the dielectric material located in an area which is not covered with the mask; a mask removing process of removing the mask from the first surface of the dielectric material; a conductor formation process of forming a conductive thin film over the whole of the first surface of the dielectric material; a bonding process of bonding the first surface of the dielectric material over which the conductive thin film is formed to a bonding surface of a substrate; and a second etching process of etching a second surface of the dielectric material which is on the opposite side to the first surface.
 12. The method according to claim 11, wherein a plurality of the recording areas exist on the first surface, and the method comprises a division process of dividing a structure produced by bonding the dielectric material and the substrate to each other into a plurality of parts so as to separate the plurality of the recording areas from each other, after the second etching process.
 13. The method according to claim 11, comprising: a measurement process of measuring an etched amount of the dielectric material in the second etching process; and a control process of controlling the second etching process on the basis of the etched amount measured by said measurement process.
 14. The method according to claim 11, comprising: a concave portion formation process of forming a concave portion on the bonding surface of the substrate before the bonding process.
 15. The method according to claim 11, wherein, in the first etching process, the first surface of dielectric material is etched by dry etching method.
 16. The method according to claim 11, wherein, in the second etching process, the second surface of the dielectric material is polished by mechanical polishing method.
 17. The method according to claim 11, wherein the second etching process comprises: a mechanical polishing process of polishing the second surface of the dielectric material by using a mechanical polishing method; and a dry etching process of etching the second surface polished in the mechanical polishing process by using a dry etching method.
 18. The method according to claim 17, wherein the second etching process comprises: a wet etching process of performing wet etching after the dry etching process.
 19. An apparatus for producing a dielectric recording medium for recording information in a dielectric material, the apparatus comprising: a mask formation device for forming a mask on a first surface of the dielectric material to cover a recording area with the mask; a first etching device for etching the first surface of the dielectric material to remove a predetermined amount of the dielectric material located in an area which is not covered with the mask; a mask removing device for removing the mask from the first surface of the dielectric material; a conductor formation device for forming a conductive thin film over the whole of the first surface of the dielectric material; a bonding device for bonding the first surface of the dielectric material over which the conductive thin film is formed to a bonding surface of a substrate; and a second etching device for etching a second surface of the dielectric material which is on the opposite side to the first surface.
 20. The apparatus according to claim 19, wherein a plurality of the recording areas exist on the first surface, and the apparatus comprises a division device for dividing a structure produced by bonding the dielectric material and the substrate to each other into a plurality of parts so as to separate the plurality of the recording areas from each other, after an etching process with the second etching device.
 21. The apparatus according to claim 19, comprising: a measurement device for measuring an etched amount of the dielectric material; and a control device for controlling the second etching device on the basis of the etched amount measured by said measurement device.
 22. The apparatus according to claim 19, comprising: a concave portion formation device for forming a concave portion on the bonding surface of the substrate before a bonding process with the bonding device.
 23. The apparatus according to claim 19, wherein the second etching device comprises: a mechanical polishing device for polishing the second surface of the dielectric material by mechanical polishing method; and a dry etching device for etching the second surface polished in the mechanical polishing process by dry etching method. 